Fluoropolymers are often utilized as processing aids in the melt processing of polymeric materials, such as polyolefins. The polymeric materials possess certain viscoelastic characteristics that, when melt processed, may result in undesirable defects in the finished material. This is particularly evident in extrusion processes for a given extrudable polymer where there exists a critical shear rate above which the surface of the extrudate exhibits melt defects. The melt defects may be present as a rough surface on the extrudate, commonly referred to as melt fracture. Melt fracture is primarily a function of the rheology of the polymer and the temperature and speed at which the polymer is processed. Melt fracture may take the form of “sharkskin”, a loss of surface gloss, that in more serious manifestations appears as ridges running more or less transverse to the extrusion direction. The extrudate may, in more severe cases, undergo “continuous melt fracture” where the surface becomes grossly distorted.
Fluoropolymers are capable of alleviating melt fracture in many polymeric materials. The fluoropolymers are incorporated into the polymeric materials in an amount generally of about 2% by weight or less.
Melt processable polymeric materials, hereinafter referred to as polymeric binders, are often combined with certain fillers or additives to both enhance the economics and to impart desired physical characteristics to the processed material. The fillers may include various organic material or inorganic material mixed throughout the polymeric host material. For example, wood flour or wood fibers are often included with certain hydrocarbon polymers to make a composite that is suitable as structural building material upon melt processing.
The incorporation of conventional fillers and additives may adversely affect the efficacy of the fluoropolymers incorporated into the melt processable mixture as a processing aid. Such fillers can interfere with the ability of the fluoropolymer to reduce melt fracture. Thus, melt fracture may occur at processing speeds that are undesirably low. Additionally, an increase of the amount of processing aid in the polymeric mixture does not reduce the melt fracture of the polymeric material to acceptable levels. For purposes of the present invention, the fillers and additives hereinafter will be referred to as interfering components.